1. Field of the Invention
The present invention relates generally to the field of semiconductor devices, and, more particularly, the present invention relates to an improved semiconductor package and method of manufacturing a package comprising an improved reinforcing plate and ground plane.
2. Description of the Related Art
There are known semiconductor devices with a structure wherein electrodes of a semiconductor element are bonded to edges of leads (interconnecting films) of a film circuit. A gap between the semiconductor element and the film circuit is filled up with sealing resin and a ring-shape reinforcing plate is adhered to the back surface of the film circuit for enclosing the semiconductor element.
FIGS. 5(A) and 5(B) are cross-sectional views of semiconductor devices manufactured in accordance with two different typical conventional technologies. First, the semiconductor device shown in FIG. 5(A) is explained. Notation a shown in the figure denotes a film circuit and notation b is a polyimide tape used as the base of the film circuit. Notation c denotes a interconnecting film serving as a lead and notation d is an insulating layer for selectively covering the surface of the film circuit a on the opposite side from the base b. The insulation film d is typically made of solder resist. Notation e is a solder ball formed on an opening f of the insulating layer d. Protruding on the surface of the lead c, the solder ball e is used as an external pin of the semiconductor device.
Notation g denotes a semiconductor element. Each electrode of the semiconductor element g is bonded to the edge of a portion of a lead c which protrudes to a device hole h. Notation i is sealing resin filling up a gap between the semiconductor element g and the film circuit a. Notation j is a reinforcing plate having the shape of a rectangular ring. The reinforcing plate j is adhered to the back surface of the film circuit a by adhesive agent k at a position enclosing the semiconductor element g.
Next, the semiconductor device shown in FIG. 5(B) is explained. Notation a' denotes a film circuit. Interconnecting films c each serving as a lead are formed on the back surface of a polyimide tape b which is used as the base of the film circuit a'. Through the polyimide tape b, openings f are bored to allow the leads c to protrude. On each of the openings f, a solder ball e serving as an external terminal is formed. Much like the semiconductor element g shown in FIG. 5(A), the semiconductor element g is connected to the lead c of the film circuit a'. A gap between the semiconductor element g and the film circuit a' is filled up with sealing resin i. A reinforcing plate j having the shape of a rectangular ring is adhered to the back surface of the film circuit a' by adhesive agent k.
The components composing the semiconductor device are assembled by using the following method. First of all, the semiconductor element g is attached to the film circuit a (a'). Then, the gap between the film circuit a (a') and the semiconductor element g is sealed with the resin i. Later on, the reinforcing plate j is adhered to the back surface of the film circuit a (a'). Then, the solder ball electrode e to be used as an external terminal is formed.
In the conventional technology shown in FIG. 5, the electrical connection between the film circuit a (a') and the reinforcing plate j does not exist, hence, resulting in the problem that it is difficult to prevent the introduction of noise from an external source and the structure itself generates electrical noise to the external world.
In addition, according to this conventional technology, after the semiconductor element g has been attached to the film circuit a (a'), the gap between them is sealed with the resin i and then the reinforcing plate j is adhered to the back surface of the film circuit a (a'). The adhesive agent k which juts out significantly resulting in a problem that, in some cases, the jutting out adhesive agent prevents the installation of the reinforcing plate j. In order to solve this problem, it is necessary to use a reinforcing plate j with an excessively large hole 1 bored thereon as shown in FIG. 5 (B). However, such a hole 1 is not desirable because the large hole 1 causes degradation in the effectiveness of the reinforcing plate j. That is to say, the semiconductor device shown in FIG. 5(B) inevitably causes the effectiveness of the reinforcing plate j to deteriorate.
In other related art approaches to chip manufacturing, the processes relied upon TAB bonding which requires a very thin resinous film and various treatments and processing of the film. This results in difficulty in the patterning of the lead limits the ability to achieve physically small leads or an increase in the number of leads. Additionally, accuracy is lower because the base used in such a process is easily bent. The present invention overcomes these disadvantages through the use of a stiff metal base.
Furthermore, in the related art processing of TAB devices, patterning by laser beam is required which is both expensive and time consuming. The problem of how to make a hole in the insulating film also is significant problem in such processes. The present invention overcomes these shortcomings by selective formation of the insulating film. Therefore patterning of the film to make holes is not required. Additionally, the surface for adhering an elastomer or a chip or a reinforcing plate had an unevenness or a level difference between the leads and the insulating film which results in difficulty in adhering and produces voids. Water disadvantageously can enter through such voids. The present invention also overcomes these shortcomings by providing a co-planar structure which has leads embedded in the insulating film. Additionally, previous related art processing required gold leads because a strong mask was required for etching. The present invention has a lead frame which is made from a metal layer having a good mechanical strength so that only copper is required.
The present invention is intended to solve the problems described above. It is thus an object of the present invention to provide a semiconductor device that has an improved noise-reduction characteristic and allows a reinforcing plate to be attached to a film circuit without any difficulty. Other objects and advantages of the present invention will be apparent from the following summary and detailed description of the preferred embodiments when viewed in light of the drawings.